The registering of the current position of a vehicle in a defined region is of great importance in a very wide range of applications. For example the determination of the positions of industrial goods-handling vehicles (e.g. forklift trucks) in the field of storage logistics (management of e.g. production stores, distribution stores) is of great importance, since by this means, for example, the optimisation of logistical processes and automatic tracing of batches of goods items is made possible. For this purpose a very wide variety of methods and devices are of known art, wherein in particular it is of known art to register an absolute reference position of the vehicle, and also the relative movement of the vehicle, and thus to determine the current position of the vehicle, with the aid of a dead reckoning navigation system.
From DE 102 34 730 A1 a method for determining the position of a transport vehicle within an effective range is of known art, in which moveable first objects, transported by the transport vehicle, (transport units, pallet cages, beverage crates or similar) and stationary second objects (for example, walls, supporting pillars) are present. The effective range is stored in the form of a digital map, which contains the positions of the objects. The forklift truck has a laser radar (=LADAR), an electronic compass, and a kinematic GPS, connected with an on-board computer, which supply data to the on-board computer. For purposes of determining the position of the forklift truck the LADAR scans a contour of the environment and thereby registers the warehouse goods items located in the immediate environment, whereupon the result of this scan is compared with the digital map stored in a central computer; on the basis of this comparison the on-board computer or the central computer can determine a position of the forklift truck within the effective range. The LADAR also registers the separation distance between the forklift truck and the known objects, in order to generate an image of the forklift truck's environment. From the determined measurements the position of the forklift truck is determined by a comparison with the data of the digital map using trigonometrical calculations and methods. For purposes of improving the determination of position, data for moveable third objects can also be held in the digital map; these are registered during the scan and are used to update the database. These third objects can be other transport vehicles and/or unknown obstacles.
Disadvantageously the objects called upon for purposes of registering position must have a measurable contour so as to enable a determination of position by way of the laser scanning procedure. Therefore identical objects (e.g. supporting pillars, Euro-pallets, etc) cannot be uniquely identified. Moreover in accordance with DE 102 34 730 A1 it is necessary to determine differences between the scans made by the vehicle and the centrally managed map so as to determine from these the exact position. This means that an exact determination of absolute position is not possible, instead a probable position is determined by way of an exclusion method; while in the best-case scenario this does indeed correspond to the actual absolute position, it can also deviate significantly from the latter. The determination of position by means of laser radar scanning in accordance with known art encounters its limitations in particular if the environment is similar or the distances involved prevent or place limits on the scanning procedure (e.g. in the case of an empty warehouse with supporting pillars, with empty storage areas, or storage areas with stored goods items that have identical structures, or in the external environment).
From US 2009/0198371 A1 a system for goods items tracking is furthermore of known art, with a fixed base system and mobile systems that are linked with vehicles. The mobile system has an identification sensor for purposes of registering objects with coding. The monitored space is also fitted with position markers that are individually different; these are arranged in the ceiling region. The vehicle has an optical position sensor device with a camera that is upwards directed; this records images of the environment so as to register position markers present in the visual field and to establish their identities. The positions of the position markers in the recorded image are used to register the position and the angular orientation of the vehicle. When a position marker is registered the database in the memory of a mobile computer system on the vehicle is also updated. However, this system has the disadvantage that no determination of position is possible if there is no marker in the field of view of the camera, i.e. no other system is available to execute a determination of position. Accordingly a marker must be in the field of view at all locations where a position is required. In storage depots, however, a registration of position is required at all locations and at all times, in order to track even goods items that are set down in unscheduled storage areas. This in turn means that the storage depot must be fitted with very many markers; this leads to an extremely high level of expenditure, particularly in the case of large storage depots. Moreover, by virtue of the attachment of markers to the ceiling, this system of known art is disadvantageously limited to an internal environment.
From DE 44 29 016 A1 a navigation system for driverless vehicles, in particular for transport systems in workshops, is of known art, in which high-contrast objects in the environment, in particular ceiling lights, are recorded by means of an imaging sensor that moves with the vehicle. From the location of these ceiling lights the position and angle of orientation of the vehicle are then determined. Through the use of the high-contrast ceiling lights for the registration of an absolute reference position the costs of the navigation system are to be kept low.
Apart from the fact that is in actual fact not possible to differentiate between ceiling lights that are usually of identical design by way of an optical sensor, e.g. using a CCD camera or photodiode array, or at best only with a high error rate, a trailing wheel is provided for purposes of registering the relative movement of the driverless vehicle; this is connected with the vehicle via a vertical axis about which it can rotate. From the angle of rotation of the wheel about its own axis, and from the angle of rotation of the horizontal movement about the vertical axis, the position of the vehicle is to be determined by way of dead reckoning navigation. In practice, however, such trailing wheels have proved to be extremely inaccurate (in particular as a result of problems with slip and drift).
From WO 01/13192 A1 a method and a device for purposes of registering the position of a vehicle are furthermore of known art, in which reflecting markers must have been previously fitted on the ceiling of a warehouse; these can be registered by the vehicle as it drives underneath a marker, so that by this means a reference position can be registered and stored at this point in time. Moreover in accordance with the WO document a wheel encoder is provided, which at intervals of time registers the distance covered by the vehicle; furthermore the angle of rotation of the vehicle is registered by means of a gyroscope. The current position of the vehicle can then be determined by means of dead reckoning navigation from the reference position and the relative distance covered, determined by means of vector addition. What is particularly disadvantageous here is the fact that the installation of the reflecting markers in the ceiling region of a warehouse is very labour and cost intensive, and moreover the registration of the reference position is not always reliably guaranteed. Furthermore problems arise in the measurement of the relative movement by means of the wheel encoder and gyroscope in terms of slip and drift of the vehicle (e.g. spinning of the wheels), so that often the relative distance covered is incorrectly determined. An application of this method in an external environment (with no roof) of a storage depot is impossible, or only if linked with substantial installation and cost expenditures.
In order to eliminate these disadvantages in the registration of relative movement it is proposed in EP 1 916 504 A2 to register digital image data of a reference surface area of sequential discrete frames, then to subdivide the first of two sequential frames into a plurality of macro-blocks, so as to determine these macro-blocks subsequently in the second frame, wherein the relative movement of the vehicle can be determined as a function of the movement vectors of the positions of the macro blocks. By this means the measurement inaccuracies, which occur during the determination of the relative movement by means of a wheel encoder and a gyroscope, can indeed be eliminated. As a result of the fact that the camera must be attached near the floor, contamination of the camera optics occurs to a large extent; this can lead to a high level of inaccuracy, or a failure, in the registration of the relative movement. However, what is particularly disadvantageous, even in the case of EP 1 916 504, is the fact that, now as before, for purposes of registering the absolute reference position a very laborious and cost intensive installation of reflecting markers in the ceiling region is required.
A similar method and a similar device for purposes of registering a reference position of a vehicle in a warehouse is furthermore of known art from US 2007/10143006 A1. Here a multiplicity of transponders are fitted to the floor of the warehouse, with the help of which a reference position of the vehicle is then to be determined. Here too this takes the form of a technically complex system with a multiplicity of sensors, which, in particular in cases where large surface areas are to be defined, are the cause of extremely high installation and investment expenditures. However, what is particularly disadvantageous is the fact that the registration of a reference position of a vehicle is only possible if it drives over a transponder, and thus there is no continuous registration of a reference position of a vehicle; this has a particularly disadvantageous consequence when e.g. setting down goods items in areas of the storage depot that are not fitted with transponders.
In DE 103 46 596 A1 is likewise proposed the registration of an absolute reference position with the aid of measurement strips that have previously been laid down. Furthermore with the aid of an incremental position registration device a relative determination of position is undertaken by the vectorial summation of incremental movement vectors, wherein a parameter is determined for purposes of displaying the quality of the absolute position registered. As a function of the quality of this parameter the position of the vehicle in the prescribed region is outputted either in absolute mode or in incremental mode, i.e. disadvantageously the absolute and relative measured data are not merged together; instead the measurement of poorer quality is totally rejected.
From US 2007/0150111 A1 an omni-directional robot is also of known art, which on its underneath side has a so-called “optical flow” sensor, with which the relative movement of the robot is registered. Here, however there is no provision for the registration of a reference position in a predefined region.